An electron vortex beam (EVB) is a type of charged particle beam where the particles are constrained to follow a helical trajectory around the propagation axis. The resulting beams have unique properties which make them useful for various applications, such as microscopy, material processing and medical therapy.
The first EVBs were generated in the late 1990s and early 2000s by passing an electron beam through a spiral phase plate. This technique was later refined using holographic optical elements, which allowed for better control over the shape and properties of the resulting beam.
One of the main advantages of EVBs is their ability to maintain a high degree of coherence over long distances. This makes them particularly well suited for use in transmission electron microscopes (TEMs), where they can be used to generate images with very high resolution. In addition, EVBs can be used to create three-dimensional images of objects without the need for tomographic reconstruction techniques.
EVBs also have potential applications outside of microscopy. For example, they could be used for precise machining or deposition of materials at the nanoscale. Additionally, recent work has shown that EVBs can be used to deliver high doses of radiation to cancer cells while sparing healthy tissue, making them promising candidates for use in cancer therapy.